Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$68.58	6.281%	$72.8875	$72.89	$72.90	$72.90
Purchase #2	$79.77	13.779%	$90.7615	$90.76	$90.75	$90.80
Purchase #3	$71.64	9.106%	$78.1635	$78.16	$78.15	$78.20
Purchase #4	$209.45	11.685%	$233.9242	$233.92	$233.90	$233.90
Purchase #5	$234.92	5.217%	$247.1758	$247.18	$247.20	$247.20
Purchase #6	$140.80	6.389%	$149.7957	$149.80	$149.80	$149.80
Purchase #7	$91.65	6.466%	$97.5761	$97.58	$97.60	$97.60
7 purchase totals =	$896.81		$970.2843	$970.29	$970.30	$970.40